Fully Passivated AlInN/GaN HEMTs With $f_{\rm T}/f_{\rm MAX}$ of 205/220 GHz

We report the fabrication and characterization of 30-nm-gate fully passivated AlInN/GaN high-electron mobility transistors (HEMTs) with cutoff frequencies f_T and f_MAX simultaneously exceeding 200 GHz at a given bias point. The current gain cutoff frequency does not vary significantly for 2.5 <; V_DS <; 10 V, while f_MAX reaches a maximum value of f_MAX = 230 GHz at V_DS = 6 V. This is the first realization of fully passivated AlInN/GaN HEMTs with f_T/f_MAX ≥ 205 GHz, a performance enabled by the careful shaping of the gate electrode profile and the use of a thin 60-nm SiN encapsulation film.